1. Field of the Invention
The present invention relates to a field emitter having a carbon nanotube film, a method of fabricating the same, and a field emission display device using the field emitter, and more particularly, to a field emitter having a carbon nanotube film for use as an electron emitting unit, a method of fabricating the field emitter, and a field emission display device using the field emitter.
2. Description of the Related Art
Field emission display devices, which are studied at present as a next-generation flat display device, are based on emission of electrons in a vacuum, and emit light by electrons emitted from micron-sized tips in a strong electric field, accelerating, and colliding with a fluorescent material. The field emission display devices are thin and light with high brightness and high resolution.
Conventional electron emitters for field emission display devices use tips made of metal or silicon, but have very complicated structures and provide a non-uniform current density between pixels. In order to solve the above drawbacks, a metal oxide semiconductor field effect transistor (MOSFET) can be used as an active circuit for each unit pixel, which is disclosed in the paper by S. Kanemaru et al., xe2x80x9cActive Matrix of Si Field Emitters Driven by Built-in MOSFETSxe2x80x9d, IDW""97, pp 735-738, 1997. Also, a thin film transistor can be used as an active circuit for each unit pixel in order to solve the above drawbacks, which is disclosed in the paper by H. Gamo et al., xe2x80x9cActively-Controllable Field Emitter Arrays with Built-in Thin-Film Transistors on Glass for Active-Matrix FED Applicationsxe2x80x9d, IDW""98, pp 66-770, 1998. However, the structures disclosed in the above papers become more complicated by adding some processes to a fabrication process for an existing field emission display device.
An objective of the present invention is to provide a field emitter having a high current density even at a low voltage using a carbon nanotube film.
Another objective of the present invention is to provide a method of manufacturing a field emitter having a carbon nanotube film through a simple process.
Still another objective of the present invention is to provide a field emission display device having a field emitter having a high current density even at a low voltage using a carbon nanotube film.
To achieve the first objective the present invention provides a field emitter having a carbon nanotube film, including: an insulating substrate; a thin film transistor formed on the insulating substrate, the thin film transistor having a semiconductor layer, a source electrode, a drain electrode and a gate electrode;
and an electron emitting unit formed of a carbon nanotube film on the drain is electrode of the thin film transistor.
The semiconductor layer of the thin film transistor can be a polycrystalline silicon layer or an amorphous silicon layer. The thin film transistor can be a coplanartype transistor, a stagger-type transistor, or an inverse stagger-type transistor.
The surface of a portion of the drain electrode, which is to contact the carbon nanqtube film, contains catalytic metal which is transition metal, such as nickel or cobalt, for carbon nanotube growth. Alternatively, the drain electrode itself is formed of catalytic metal for growing carbon nanotubes.
To achieve the second objective, the present invention provides a method of manufacturing a field emitter having a carbon nanotube film, the method including:
forming a thin film transistor having a semiconductor layer, a source electrode, a drain electrode and a gate electrode on an insulating substrate; forming a protective insulating film on the entire surface of the insulating substrate on which the thin film transistor has been formed; etching part of the protective insulating film to expose part of the drain electrode; and forming a carbon nanotube film on the exposed drain electrode, When the thin film transistor is a coplanar-type transistor, the step of forming the thin film transistor includes the substeps of: forming a semiconductor layer on the insulating substrate; forming a source electrode pattern and a drain electrode pattern separated a predetermined distance from each other on the semiconductor layer; and forming a gate electrode pattern consisting of a gate insulating film and a gate electrode, between the source electrode pattern and the drain electrode pattern. When the thin film transistor is a stagger-type transistor, the step of forming the thin film transistor includes the substeps of: forming a source electrode pattern and a drain electrode pattern separated a predetermined distance from each other on the insulating substrate; forming a semiconductor layer pattern extending a predetermined length to the sides while filling the space between the source electrode pattern and the drain electrode pattern; and forming a gate electrode pattern consisting of a gate insulating film and a gate electrode, on the semiconductor layer pattern between the source electrode pattern and the drain electrode pattern. When the thin film transistor is an inverse stagger-type transistor, the step of forming the thin film transistor includes the substeps of: forming a gate electrode pattern consisting of a gate electrode and a gate insulating film, on the insulating substrate; forming a semiconductor layer pattern which covers the gate electrode pattern; and forming a source electrode pattern and a drain electrode pattern separated a predetermined distance from each other on the semiconductor layer pattern.
The step of forming a carbon nanotube film on the exposed portion of the drain electrode can be performed by coating the surface of the exposed portion of the drain electrode with an already-grown carbon nanotube film, or by directly growing the carbon nanotube film on the surface of the exposed portion of the drain electrode. At this time, the method further includes forming a catalytic metal layer for carbon nanotube growth on the surface of a portion of the drain electrode which contacts the carbon nanotube film. The step of forming the catalytic metal layer is performed in the step of forming the thin film transistor or after the step of etching part of the protective insulating film.
To achieve the third objective, the present invention provides a field emission display device in which unit pixels, each of which is defined by a plurality of gate lines and a plurality of data lines which cross at right angles, are arrayed in a matrix, wherein each of the unit pixel includes: a thin film transistor formed on an insulating substrate, the thin film transistor having a semiconductor layer, a source electrode, a drain electrode and a gate electrode; n electron emitting unit formed of a carbon nanotube film on the drain electrode of the thin film transistor; an upper electrode formed opposite to the insulating substrate; and a fluorescent material formed on the bottom surface of the upper electrode, opposite to the electron emitting unit.
In the present invention, a carbon nanotube film is used as an electron emitting unit of a field emitter, so that a field emitter having a high current density even at a low voltage can be realized by a simple manufacturing method. A field emission display device having a uniform current density in each pixel can be realized since it is driven by a thin film transistor.